This invention relates to fiber-reinforced plastic resin compositions. It is well known that the incorporation of reinforcing fibers into polymeric products beneficially affects resin properties such as tensile strength, Izod impact strength, flexural modulus, stiffness, dimensional stability and resistance to creep and thermal expansion.
In reaction spray molding applications, glass roving is chopped and sprayed onto a form with the resin. However, in injection or cast applications, the chopped glass fibers must be blended with the resin prior to injection or casting. Typically, this is done by placing chopped fibers and resin granules in an extrusion hopper or screw plasticating injection hopper together and blending them as the resin is heated. The problem is, the fibers tend to be pulverized in the process, reducing their effectiveness as reinforcement. Some melt the polymer first and then introduce the chopped fibers. This is better, but more expensive. Blending must still be accomplished, and the blending breaks up the fibers.
Typically, reinforcing fibers as supplied by the manufacturers are sized or coated in order to improve handling and provide a tie coat to improve adhesion between the reinforcing fiber and the resin matrix. Despite the coating, it is difficult in injection molding or extrusion applications to compound the fibers with the resin without breaking the fibers to such an extent that their reinforcement capability is severely diminished.